Influenza A (H1N1) 2009 vaccine: efficacy and safety

influenza-vaccineThere have been many interesting responses to my recent post, “Are you receiving the influenza 2009 H1N1 vaccine?” Some individuals have already been immunized or plan to do so shortly. Others are concerned about the safety and efficacy of the monovalent preparations. As pointed out recently in a Nature editorial, “Mass-vaccination campaigns…must take public concerns into account”, and “officials should focus on providing people with the information they need to make good choices for themselves.” Here are some facts about the influenza H1N1 vaccine for those who haven’t yet made up their minds whether or not to be immunized.

Four companies are licensed to produce the 2009 H1N1 influenza vaccine for the US – CSL Limited, Novartis Vaccines, Sanofi-Pasteur Inc., and MedImmune. The US Food & Drug Administration has published on their website the package insert for each product. These are multipage documents with a good deal of information, including indications, dosage, contraindications, adverse reactions, and the results of clinical studies. Links to the package insert for each vaccine are listed below.

  • CSL Limited – Afluria Influenza A (H1N1) 2009 Monovalent Vaccine (pdf)
  • Novartis Vaccines and Diagnostics – Fluvirin Influenza A (H1N1) 2009 Monovalent Vaccine (pdf)
  • Sanofi Pasteur, Inc – Fluzone Influenza A (H1N1) 2009 Monovalent Vaccine (pdf)
  • MedImmune LLC – Flumist Influenza A (H1N1) 2009 Monovalent Vaccine (pdf)

For example, the package insert for Afluria indicates that the vaccine is supplied as a sterile suspension for intramuscular injection in two forms: a 0.5 mL preservative-free, single-dose, pre-filled syringe; and a 5 mL multi-dose vial containing ten doses. Thimerosal, a mercury derivative, is added as a preservative in the multi-dose vial; each 0.5 mL dose contains 24.5 micrograms of mercury.

The results of two clinical studies on the safety and efficacy of Afluria are also reported: a US study of 1,357 individuals, and a UK study of 275 subjects. No serious adverse effects were reported in either study. The seroconversion rates are included in the form of hemagglutination-inhibition titers.

I encourage everyone to read at least one of these package inserts to become familiar with the extent to which these vaccines have been tested in people. If any aspects of these documents are not clear, don’t hesitate to contact me.

Note added after publication: It was pointed out in the comments that the safety and efficacy data reported in the package inserts were obtained with the seasonal influenza vaccines, Afluria, Fluvirin, Fluzone, and Flumist, not the 2009 monovalent H1N1 vaccine. My apologies for implying otherwise. I will locate the safety and efficacy data for the monovalent H1N1 vaccines and update the post with that information.

Second addendum: According to the FDA, the influenza A (H1N1) 2009 monovalent vaccine has been tested in the same way as new seasonal vaccines that are produced each year. The inactivated influenza A (H1N1) monovalent vaccine manufactured by CSL Limited was tested in 120 adults. By day 21 after vaccination, HI antibody titers of 1:40 or more were observed in 116 (97%) of 120 adults who received a 15 μg dose. Injection site tenderness or pain was reported by 46% of subjects, while 45% of the subjects reported one or more systemic symptoms (headache, malaise, or myalgia). These observations are similar to those observed in testing of seasonal influenza vaccines. The preliminary results have been published.

The Sanofi Pasteur 2009 H1N1 vaccine has been tested in children aged 6-35 months, 3-9 years, and 10-17 years, and the results have been reported by NIAID. After immunization with a single 15 μg dose of vaccine, 25%, 36% and 76% of individuals in each age group developed HI antibody titers of 1:40 or more. No information on adverse effects have been provided.

Medimmune and Novartis have reported immunogenicity and safety study results similar to those observed for seasonal vaccines, but the data have not yet been released.

Although the 2009 H1N1 vaccines produced by all four manufacturers have been approved by the FDA, all the data used for approval have not yet been published or released. As soon as these data are available I will pass them on.